EP0921836B1

EP0921836B1 - Apparatus for treating adult-onset dementia of the alzheimer's type

Info

Publication number: EP0921836B1
Application number: EP97932542A
Authority: EP
Inventors: Edward Rubenstein; David L. Karshmer; Elliott C. Levinthal; Jaime S. Vargas; Tom A. Saul
Original assignee: Eunoe Inc
Current assignee: Eunoe Inc
Priority date: 1996-07-11
Filing date: 1997-07-10
Publication date: 2004-05-12
Anticipated expiration: 2017-07-10
Also published as: CA2260250A1; US6264625B1; JP2002514096A; DE69729102T2; DE69729102D1; EP0921836A1; AU3597497A; US5980480A; WO1998002202A1; ES2219771T3

Description

BACKGROUND OF THE INVENTION

This invention relates generally to an apparatus for treating patients with adult-onset dementia. In particular, the invention relates to an apparatus for increasing the clearance of substances from the cerebrospinal fluid in certain patients with adult-onset dementia of the Alzheimer's type.

The brain and spinal cord are encased within the cranium and vertebral column inside a thin membrane known as the arachnoid. The volume of the intracranial space is on average about 1700 ml. The volume of the brain is approximately 1400 ml, the volume of the intracranial blood is approximately 150 ml, the remaining 150 ml is filled with cerebrospinal fluid. The cerebrospinal fluid circulates within the subarachnoid space. It is formed principally by the choroid plexuses, which secrete about 80% of the total volume. The sources of the remainder are the vasculature of the subependymal regions, and the pia mater. The total volume of the cerebrospinal fluid is renewed several times per day, so that about 500 ml are produced every 24 hours.

The cerebrospinal fluid is absorbed through the arachnoid villi, located principally over the superior surfaces of the cerebral hemispheres. Some villi also exist at the base of the brain and along the roots of the spinal nerves. The absorptive processes include bulk transport of large molecules and as well as diffusion across porous membranes of small molecules. (Adams et al. (1989) "Principles of Neurology," pp. 501-502).

The principle on which this invention is based is that in some persons with adult-onset dementia of the Alzheimer's type there is dysfunction of the cerebrospinal fluid resorptive mechanism, leading to the retention in the cerebrospinal fluid of substances which result in the histologic lesions associated with adult-onset dementia of the Alzheimer's type, or which are neurotoxic, or both.

There are several examples of low-molecular weight proteins or peptides that are known to be present in elevated concentrations in the cerebrospinal fluid of persons suffering from adult-onset dementia of the Alzheimer's type. For example, elevated levels of beta A-4 amyloid have been found in the cerebrospinal fluid of patients with early-onset Alzheimer's disease. (Nakamura et al., (1994) "Amyloid beta protein levels in cerebrospinal fluid are elevated in early-onset Alzheimer's disease," Ann. Neurology 36:903-911). Beta A-4 amyloid is known to self-aggregate into molecules of amyloid of the type that typify the core plaques found in the brain in persons suffering from adult-onset dementia of the Alzheimer's type. In fact, beta A-4 amyloid deposition in the brain is the only microscopic lesion specific for Alzheimer's disease. Furthermore, beta A-4 amyloid has been shown to be neurotoxic. (Bush et al., (1992) "Beta A-4 amyloid protein and its precursor in Alzheimer's disease," Pharmac. Tera. 56:97-117). Beta A-4 amyloid is also a component of microscopic cerebral lesions known as neurofibrillary tangles, characteristically found in adult-onset dementia of the Alzheimer's type.

Beta-2 microglobulin is another example of a low-molecular-weight protein whose concentration in the cerebrospinal fluid increases with age and reaches high levels in patients with adult-onset dementia of the Alzheimer's type. (Martinez et al., (1993) "Relationship of interleukin-1 beta and beta₂-microglobulin with neuropeptides in cerebrospinal fluid of patients with dementia of the Alzheimer type," J. Neuroimmunology 48:235-240). Beta-2 microglobulin is associated with amyloid deposits in some tissues of patients on long-term renal hemodialysis. (Ono et al., (1994) "Formation of amyloid-like substance from beta-2-microglobulin in vitro. Role of serum amyloid P component: a preliminary study," Nephron 66:404-407).

Another substance that accumulates in the cerebrospinal fluid in patients with adult-onset dementia of the Alzheimer's type is tau, a component of the neurofibrillary tangles found in involved brain tissue. Tau concentrations in cerebrospinal fluid are regularly increased in this syndrome with eight fold increases present in half of the patients. (Arai et al., (1995) "Tau in cerebrospinal fluid: a potential diagnostic marker," Ann. Neurology 38:649-652).

In addition, the prior art also describes devices used to remove cerebrospinal fluid from a patient. Matkovich U.S. Patent No. 5,334,315 describes a method and device that can be used to remove a body fluid from a patient, to treat that fluid to remove an undesirable component, and to return the fluid to the patient. Matkovich's partial list of the kinds of deleterious or undesirable substances that can be removed from a fluid includes proteins, polypeptides, interleukins, immunoglobulins, proteases and interferon. The fluids from which these substances can be removed using the Matkovich apparatus include cerebrospinal fluid, blood, urine and saliva. Matkovich never suggests, however, that his method and apparatus could be used to treat patients suffering from adult-onset dementia of the Alzheimer's type.

Kirsch et al. U.S. Patent No. 5,385,541 describes a cerebrospinal fluid shunt mechanism used to treat hydrocephalus by draining cerebrospinal fluid into the patient's abdomen, chest or vascular system. The system may include a one-way valve to prevent backflow. Kirsch et al. does not describe the use of such a system to treat adult-onset dementia of the Alzheimer's type, however.

Ruzicka et al. U.S. Patent No. 4,950,232 discloses another cerebrospinal fluid shunt system. As with the Kirsch et al. patent, Ruzicka does not suggest the use of his shunt system to treat adult-onset dementia of the Alzheimer's type.

Chen et al. (1994) "Effectiveness of Shunting in patients with normal pressure hydrocephalus predicted by temporary, controlled-resistance, continuous lumbar drainage: a pilot study," J. Neurol. Neurosurg. Psychiatry 51:1430-1432, describes use of a "silicon" catheter for draining CSF from the subarachnoid region into an external collection bag.

DISCLOSURE OF THE INVENTION

Although the prior'art has recognized the presence of elevated concentrations of certain substances in the cerebrospinal fluid of persons suffering from adult-onset dementia of the Alzheimer's type, the prior art has not provided a method of correcting this imbalance. One objective of this invention, therefore, is to enable such a treatment. Thus, the invention enables a method for treating a patient for adult-onset dementia of the Alzheimer's type by removing a portion of the patient's cerebrospinal fluid, preferably (although not necessarily) by transporting the fluid to another portion of the patient's body.

In addition, although the prior art has provided shunt devices to remove excess cerebrospinal fluid from patients suffering from hydrocephalus, the prior art has not recognized the use of these devices to treat adult-onset dementia of the Alzheimer's type by removing cerebrospinal fluid that is not excessive in volume. An objective of this invention is to provide an apparatus designed to transport cerebrospinal fluid at a controlled rate. The invention therefore provides an apparatus for removing cerebrospinal fluid as defined or claim 1.

The present invention provides apparatus for removing cerebrospinal fluid from a patient in a controlled manner, particularly for the treatment of Alzheimer's disease. The cerebrospinal fluid is preferably removed at a rate sufficient to reduce or eliminate, preferably eliminate the progression of Alzheimer's disease in patients. Usually, the removal rate will be in the range from 5% to 50% of the patient replacement rate (typically in the range from 250 ml/day to 300 ml/day), more usually from 10% to 20% of the replacement rate. At present, the preferred removal rate is in the range from 0.5 ml/hour to 15 ml/hour, preferably from 1 ml/hour to 5 ml/hour, more preferably from 1 ml/hour to 3 ml/hour, based on the average removal rate over a 24-hour period. It will be appreciated, however, that the particular removal rate which is effective with any individual patient may vary from within the preferred ranges set forth above, and any removal rate which results in significant lowering of the concentration of the factors associated with Alzheimer's disease may have a therapeutic effect.

The invention will be described in more detail below with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1A shows an embodiment of the invention in which the fluid flow rate control device is a pump.

Fig. 1B shows an embodiment of the invention in which the fluid flow rate control device is a screw pump.

Fig. 2 diagrammatically shows an embodiment of the invention providing for recirculation of the patient's cerebrospinal fluid.

Fig. 3 shows a pressure transducer for sensing cerebrospinal fluid pressure and controlling the flow rate of cerebrospinal fluid.

Figs. 4B, 4C and 4E show apparatus in which the flow rate control device is a bellows pump powered by the patient.

Fig. 4D is a sectional view of the apparatus illustrated in Figs. 4A, 4B and 4C.

Fig. 5 shows another arrangement in which the flow rate control device is a pump powered by pressure changes within the patient.

Fig. 6A is a sectional view of a pressure driven pump in an intake cycle.

Fig. 6B shows the pump of Fig. 6A during discharge.

Fig. 7A is perspective view of the pump shown in Fig. 6.

Fig. 7B is a transverse section of the pump shown in Fig. 6 diagrammatically showing inlet and outlet valves that may be incorporated therein.

Fig. 7C shows the pump of Fig. 7A during intake.

Fig. 7D shows the pump of Fig. 7A during discharge.

Fig. 8 is a cross-section of the inlet valve at the upstream end of the apparatus diagrammatically shown in Fig. 5.

Fig. 9 is a schematic illustration of a catheter system which may be used to perform the methods enabled by the present invention.

DESCRIPTION OF THE SPECIFIC EMBODIMENT

In its most general terms, the apparatus of this invention is used to treat a patient suffering from adult-onset dementia of the Alzheimer's type by removing a portion of the patient's cerebrospinal fluid. Since the patient is able to replace the removed fluid, removal of the cerebrospinal fluid has the effect of diluting the concentration of any deleterious materials in the patient's cerebrospinal fluid, such as neurotoxic substances and substances associated with histologic lesions. However, since removal of cerebrospinal fluid at too great a rate could be harmful to the patient, the invention preferably controls the rate of transport of cerebrospinal fluid.

The preferred apparatus of this invention includes a conduit or catheter having a first or inlet end portion positioned in a space within the patient's subarachnoid space, preferably in one of the lateral ventricles. The ventricles form a group of interconnected cavities that are located within the cerebral hemispheres and brain stem. These ventricles or spaces are continuous with the central canal of the spinal cord and are similarly filled with cerebrospinal fluid.

The conduit or catheter may comprise two or more distinct segments or portions, each of which is a separate tube, connector, module, or the like, as described in more detail below. The inlet portion of the catheter may be in any form which is suitable for placement within the subarachnoid space and which is capable of collecting cerebrospinal fluid from the region of the subarachnoid space. Conveniently, the form of the inlet end of the catheter may be similar or identical to conventional ventricular catheters of the type used for draining cerebrospinal fluid for treating hydrocephalus, such as those described in U.S. Patent Nos. 5,385,541 and 4, 950,232 . Suitable ventricular catheters which can be incorporated into catheter systems according to the present invention are available from commercial suppliers, such as Medtronic PS Medical, Goleta, California.

One inlet end portion construction is shown, for example, in Fig. 3 and designated with reference numeral 3. As noted above, inlet end portion 3 preferably is adapted for placement in one of the ventricles for removing cerebrospinal fluid therefrom. The end portion preferably includes multiple perforations or holes 4 spaced from the tip of portion 3. These holes preferably do not extend more than about 1 to 1.5 cm from the tip. Although a particular inlet hole arrangement is shown, arrangements can be used without departing from the scope of the invention. The conduit preferably comprises biocompatible material suitable for implantation in the patient such as implant grade low bending modulus material that is generally kink resistant. The conduit may, for example, comprise silicone or reinforced silicone, or medical shunt tubing may be used. The tubing may have an outer diameter of about 2.0 mm and an inner diameter of about 0.5-1.5 mm.

The conduit has a second end portion having an outlet or discharge opening external to the space within the patient's subarachnoid space for draining cerebrospinal fluid to other body cavities. Thus, the conduit's outlet opening is disposed in another portion of the patient's body such as in the peritoneal cavity for example. It should be recognized, however, that the second end of the conduit may also be disposed transcutaneously to lie completely external to the patient's body so that the transported cerebrospinal fluid is completely removed from the patient. In this case, the conduit may.be led subcutaneously from the head to the abdomen and exit transcutaneously from the abdomen.

The outlet or discharge portion of the conduit may, for example, be in the form of a conventional peritoneal catheter of the type used for peritoneal dialysis. Such catheters may be joined directly to the inlet portions of the catheter, e.g. be joined directly to a ventricular catheter as discussed above. In a specific embodiment, as described in more detail below, a peritoneal catheter is joined to a flow control module which in turn is joined to the ventricular catheter in order to form a catheter system suitable for draining cerebrospinal fluid according to the methods of the present invention. The flow control module will control flow rate and will usually also control flow direction, i.e. permitting flow only in the direction from the subarachnoid space to the discharge location. Provision within the flow control module may also be made for detecting flow in order to assure that the system is operating properly after implantation.

Finally, in order to control the removal rate of cerebrospinal fluid from the patient, the apparatus of this invention has a fluid flow rate control device for controlling the flow rate of fluid through the conduit (optionally embodied in a flow control module as described above). When placed in the thoracic cavity, fluid flow rate control device 10 preferably is positioned in the lateral mid-thorax near the axillary line and preferably on the under surface of a rib. It is held in place with sutures to the periosteum.

Fig. 1A shows the embodiment in which the fluid flow rate control device is an implantable pump 18 attached to conduit 2. Pump 18 may be a diaphragm pump, piston pump, rotor pump, peristaltic pump, screw pump, or any other suitable pump. The power source for pump 18 may be a battery or other energy storage device, such as a mechanical flywheel with self-winding operation. The pump also may be remotely operated as is known in the art. Pump 18 further may be operated continuously or periodically, either on demand or according to a schedule or program. Pump 18 may be mounted on a baseplate 20 which is adapted for attachment to a portion of the patient's anatomy. Fig. 1B illustrates a conventional screw pump arrangement where a screw shaft 22 is mounted for rotation within conduit 2. The drive may be positioned in a hermetically sealed package mounted to the conduit exterior and arranged within the thorax or peritoneum. The drive may be coupled to screw shaft 22 with a gear transmission as would be apparent to one of ordinary skill in the art. Other screw pump configurations also can be used such as those disclosed in U.S. Patent No. 4,857,046 to Stevens et al. to 5,372,573 to Habib.

Fig. 2 diagrammatically shows an embodiment of the invention in which a return loop is provided. In this embodiment, the fluid flow rate control device includes a bidirectional valve 24 and a pump, such as a pump 18. The pump is coupled to conduit 2 to pump fluid therethrough and the valve is fluidly coupled to the pump. Valve 24 switches the effluent of the pump between a discharge line 26, which may form part of conduit 2, and a return line, 28. The discharge line may have an outlet located within the patient's body (e.g. it may be located in the peritoneum) or exterior to the patient. Return line 28 has an outlet adapted for being located within the patient's subarachnoid space (e.g., in one of the lateral ventricles as discussed above). In this embodiment, the pump is operated substantially continuously to remove cerebrospinal fluid from, for example, the ventricles. Valve 24 is switched between

lines

26 and 28 to maintain proper pressure of the patient's subarachnoid space. Valve 24 may be operated on a time basis or on a demand basis, e.g., based on sensed cerebrospinal fluid pressure. Generally, cerebrospinal fluid removal may be undesirable at fluid pressures below about 6 cm H₂O. A pressure transducer may be used to sense that pressure and control valve 24 to control the flow rate of cerebrospinal fluid as will be described below with reference to Fig. 3.

Referring to Fig. 3, a pressure transducer 30 may be arranged on the exterior of conduit 2 in the vicinity of the tip of inlet portion 3 for sensing cerebrospinal fluid pressure. Transducer 30 may be selected to send a signal to valve 24 through leads 32 in response to sensing a signal below a threshold value of 6 cm H₂O. The valve may include a solenoid for switching the valve to the recirculation position discussed above in response to receiving the signal from the transducer. Leads 32 may be embedded in conduit 2 or otherwise coupled to the conduit and extend along the conduit to couple the transducer to the valve control mechanism or solenoid as would be apparent to one of ordinary skill. For example, leads 32 may be placed on the exterior surface of conduit 2 and thin walled shrink tubing placed around conduit 2 and leads 32 to embed the leads between the conduit and shrink tubing and secure them in position.

Referring to Fig. 4A, an apparatus in which the flow rate control device is a bellows-type pump 80 powered by the motion of the patient's diaphragm 82 is shown. Pump 80 generally includes a check valve to prevent flow of fluid back into the space within the patient's subarachnoid space and an outlet valve as will be discussed in more detail below. One end of the valve is fixed to the diaphragm and the other to some anatomy of the patient, e.g., a rib, so that when the diaphragm moves the pump moves between the positions shown in Figs. 4B and 4C.

Bellows pump 80 may be constructed as shown in Fig. 4D where the pump is illustrated in section. Bellows pump 80 generally includes end portions 85a and 85b and bellows portion 87. End portions 85a and 85b may include loops 74 to receive sutures 76 for securing the valve to the anatomy as discussed above. End portions 85a and 85b also form the housings for inlet and

outlet valves

86 and 88.

Valves

86 and 88 include spherical valve members 90 and 91 that are biased against

valve seats

92 and 93 by coil springs 94 and 95. The coil springs surround spring support posts 96 and 97 which extend from or are secured to post

support structures

98 and 99.

Structures

98 and 99 are perforated to allow cerebrospinal fluid flow therethrough.

A check valve 140 (see, e.g., Figs. 4A and 8) may form part of the flow rate control device and may be provided to maintain the desired physiologic conditions within the subarachnoid space. Valve 140 preferably is selected to close conduit 2 and prevent fluid flow therethrough when cerebrospinal fluid pressure within the subarachnoid space drops below 6 inches H₂O for example. Valve 140 preferably is positioned adjacent and external to the skull.

Referring to Fig. 8, check valve 140 comprises an upper housing portion 142 and lower housing portion 144. Upper portion 142 further includes inlet portion 146 and outlet portion 148 which define

inlet passages

150 and 152. Inlet and

outlet portions

146 and 148 preferably are arranged with their central axes being generally perpendicular to one another as shown in Fig. 8 to facilitate implantation below the dermis. Diaphragm 154, which may comprise, for example, any of the materials described above with reference to diaphragm 118, is positioned between upper and

lower portions

142 and 144, forms first chamber 156 and second chamber 158 and provides a seal therebetween. Diaphragm 154 includes a conical portion 160 for fitting within and sealing inlet passage 150 as shown in Fig. 8. Diaphragm 154 is biased toward the position shown in Fig. 8 by coil spring 162, which is positioned around post 164. Coil spring 162 is selected to allow diaphragm 154 to move away from inlet passage 150, thereby allowing cerebrospinal fluid to flow through inlet passage 150 and be discharged from outlet passage 152, when the cerebrospinal fluid pressure exceeds about 6 cm H₂O. Upper and

lower portions

142 and 144 may be. generally annular as shown in the drawings.

Returning to Fig. 4D, inlet valve 86 is a check valve and prevents backflow of cerebrospinal fluid from the pump. It is constructed to open at very low pressures (e.g., it may be designed to open at 5-10 cm H₂O). Outlet valve 88 is designed to have a cracking pressure greater than or equal to the maximum cerebrospinal fluid pressure within the subarachnoid space (the fluid pressure within this space typically ranges from about 1 to 6 cm H₂O). Thus, in this example the cracking pressure is designed to be greater than or equal to 15 cm H₂O. When valve 140 is set to open 6 cm H₂O, as discussed above, bellows pump 80 is configured to increase the fluid pressure in the bellows to a minimum of 15 cm H₂O during contraction to crack the outlet valve. These design parameters, including valve 140 being designed to open at pressures greater than or equal to 6 cm H₂O, facilitate drainage only when the patient is lying down. Valve 140 typically will see pressures less than 6 cm H₂O when the patient stands and close in response to such pressures. Although particular valve cracking pressures have been described, other preselected values may be used for operation at different postures of the patient where different intraventricular or column height pressures occur.

In operation, inlet valve 86 is open and outlet valve 88 closed when the bellows is expanded as shown in Fig. 4D and the inlet valve is fluidly coupled to cerebrospinal fluid within the subarachnoid space. Inlet valve 86 closes and outlet valve 88 opens when the bellows contracts and the cracking pressure for the outlet valve is attained.

Another apparatus where the bellows is attached to is an isolated muscle group is shown in Fig. 4E. The muscle contraction frequency is controlled by an implant electronic stimulator as diagrammatically shown in the drawing. The bellows pump may be identical in construction to bellows pump 80 described with reference to Fig. 4D as indicated in the drawing and may be secured to muscle 250 with sutures 76. Electronic muscle stimulator implant 252 may be electrically coupled to muscle 250 with leads 254 which may be sutured to the muscle as is done in implantable defibrillator placement. The sutures are made sufficiently taut to have the pump contract with the muscle. Stimulator 252 may comprise a power source programmed to deliver <1 volt (at negligible current) to effect muscle contraction as would be apparent to one of ordinary skill in the art. The frequency of excitation preferably is predetermined and may correspond to 12 to 20 cycles per minute (which corresponds to a typical breathing rate) or it may vary from that range. The stimulator preferably is designed to operate only when the patient is lying down and may include known level detection circuitry to trigger operation. Transducer 30 also may be incorporated in this embodiment to shut down stimulator 252 when the fluid pressure within the subarachnoid space is less than 6 cm H₂O or control excitation frequency depending on pressure greater than or equal to 6 cm H₂O.

Referring to Fig. 5, another flow rate control device is shown. According to this device, the flow rate control device responds to pressure changes within the patient. The flow rate control device may, for example, be driven by pressure changes in the thoracic cavity. It may be coupled to the periosteum in the same manner as described above and the outlet 8 of conduit 2 positioned in the peritoneal cavity. Flow rate control device 10 (Fig. 5) may be a piston pump as shown in Figs. 6A and 6B and designated with reference numeral 300. A diaphragm pump may be used in conjunction with a check valve such as check valve 140 (Fig. 8).

Piston pump 300 (Fig. 6A) comprises an inlet 302 passage formed in upper housing portion 303 of the pump and an outlet passage 304 formed in the pump's middle housing portion 305. Middle portion 305 defines in part inlet chamber 306 in which resides first valve member 308, which is in the form of a spherical ball. Valve member 308 is biased against valve seat 309 which is formed in upper portion 303 in the downstream end portion of inlet passage 302. Valve member 308 is biased toward valve seat 309 by coil spring 310 which surrounds and is supported by post 312.

Inlet chamber 306 is fluidly coupled to piston chamber 314 through passage 316. Piston chamber 314 is formed by the recess in piston 318 and a portion of middle portion 315 that extends therein as shown in Fig. 6A. Piston chamber 314 is sealed from the environment, such as that found in the thoracic cavity, by piston 318 (which may be generally cylindrical) and is sealingly coupled to an inner wall 321 of lower housing portion 320 (which may be annular), as shown in Fig. 6A and 6B. The seal may be formed by raised portion or rib 318a that extends from piston 318 or an O-ring, for example. Lower housing portion 320, in turn, is secured to middle portion 305 by conventional means such as welding. Passage 322 fluidly couples piston chamber 314 to outlet chamber 324 when valve member 326 is in the position shown in Fig. 6B More specifically, second valve member 326, which is in the form of a spherical ball, is biased against valve seat 327 by coil spring 328 which, in turn, is supported by post 330. As shown in the drawings, inlet and outlet chambers 306 and 324 are fluidly coupled to inlet and

outlet passages

302 and 304. Piston 318 may comprise an elastomeric material, such as polytetrafluoroethylene, or high durometer silicone.

The pressure in the thoracic cavity, which, as noted above, varies on each breath, is the driving force for piston pump 300. When the thoracic cavity pressure is low (e.g., at about -8 cm H₂O) piston 318 is drawn out and valve member 308 retracts from valve seat 307 as shown in Fig. 6A. In this position, cerebrospinal fluid flows into inlet passage 302, through inlet chamber 306 and into piston chamber 314 as indicated by arrows 332. When the pressure in the thoracic cavity increases to about -5 cm H₂O, return spring 334 forces or urges piston 318 inwardly to a closed position such that second valve member 326 moves away from valve seat 327, while first valve member 308 returns to valve seat 309 as shown in Fig. 6B. In this position, cerebrospinal fluid, designated with reference arrow 346, is discharged from piston chamber 314, through outlet chamber 324 and out from outlet 304 to conduit 2 (Fig. 5).

Referring to Figs. 6A and 6B the inlet valve, which includes ball 302, is a check valve and prevents backflow of cerebrospinal fluid from the pump (i.e., it prevents flow in the upstream direction). It is constructed to open at very low pressures (e.g., it may be designed to open at 1-6 cm H₂O). The outlet valve, which includes ball 326, is designed to have a cracking (opening) pressure greater than or equal to the maximum cerebrospinal fluid pressure within the subarachnoid space (the fluid pressure typically ranges from about 5 to 15 cm H₂O). Thus, in this example the cracking pressure is designed to be greater than or equal to 15 cm H₂O. When valve 140 is set to open at 6 cm H₂O, as discussed above, the piston and return spring 334 are configured to increase the fluid pressure in chamber 316 to a minimum of 15 cm H₂O during compression to crack the outlet valve. The pump also may be designed to accommodate the relatively low pressures typically present in the thoracic cavity. The pressure in the thoracic cavity changes from about -5 to about -8 cm H₂O during normal breathing. In view of this relatively low pressure change of about 3 cm H₂O, the piston preferably is designed to amplify the pressure available in the thoracic cavity to allow the piston to be drawn backwards and complete its outward stroke. This amplification may be about 3 to 5 fold and may be accomplished by providing an outer piston surface 336 with an area of about 3. to 5 times that of the inner working surface 338 of piston 318. As can be readily seen in Fig. 6B, outer piston surface area 336 is exposed to the environment through opening 340 and space 342 formed around and above coil support ring 344 in lower housing portion 320. These design parameters, including valve 140 being designed to open at pressures greater than or equal to 6 cm H₂O, facilitate drainage only when the patient is lying down. It should be noted, however, that other cracking pressures may be used, for example, to facilitate operation when the patient assumes other postures as discussed above with reference to bellows pump 80.

In another apparatus, the flow rate control device may be a diaphragm pump such as diaphragm pump 100 illustrated in Figs. 7A-7D. Referring to Fig. 7B, diaphragm pump 100 comprises an inlet passage 102 formed in upper housing portion 103 of the pump and an outlet passage 104 formed in the pump's middle housing portion 105. Middle portion 105 defines inlet chamber 106 in which resides first valve member 108, which is in the form of a spherical ball. Valve member 108 is biased against valve seat 109 which is formed in upper portion 103 in the downstream end portion of inlet 102. Valve member 108 is biased toward valve seat 109 by coil spring 110 which surrounds and is supported by post 112.

Inlet chamber 106 is fluidly coupled to diaphragm chamber 114 through inlet passage 116. Diaphragm chamber 114 is sealed from the environment through diaphragm 118 which is secured in place by generally ring shaped member 120. Ring shaped member 120, in turn, is secured to middle portion 105 by conventional means such as welding. Passage 122 fluidly couples diaphragm chamber 114 to outlet chamber 124 when valve member 126 is in the position shown in Fig. 13D. More specifically, second valve member 126, which is in the form of a spherical ball, is biased against valve seat 127 by coil spring 128 which, in turn, is supported by post 130. As shown in the drawings, inlet and

outlet chambers

106 and 124 are fluidly coupled to inlet and

outlet passages

102 and 104.

As with piston pump 300, the pressure in the thoracic cavity is the driving force for diaphragm pump 100. When the thoracic cavity pressure is low as compared to the pressure in chamber 114, diaphragm 118 is drawn out and valve member 108 retracts from valve seat 107 as shown in Fig. 7C. In this position, cerebrospinal fluid flows into inlet passage 102, through inlet chamber 106 and into diaphragm chamber 114 as indicated by arrows 132. When the pressure in the thoracic cavity increases such that it is greater than the pressure in chamber 114, the thoracic cavity pressure, generally indicated with reference numeral 134, forces diaphragm 118 inwardly such that second valve member 126 moves away from valve seat 127, while first valve member 108 returns to valve seat 107 as shown in Fig. 7D. In this position, cerebrospinal fluid is discharged from diaphragm chamber 114, through outlet chamber 116 and out from outlet 104 to conduit 2 (Fig. 5). As noted above, a check valve, such as check valve 140 may form part of the flow rate control device to maintain the desired physiologic conditions within the subarachnoid space. The pump inlet valve, outlet valve and diaphragm may be constructed according to the descriptions provided above with reference to the bellows and piston pump embodiments. The diaphragm also may be modified to accommodate relatively low pressure changes in the thoracic cavity.

The flow detection component 408 illustrated in Fig. 9 may be provided in a variety of ways. Most simply, a flow responsive element, such as a valve component or other element which moves in response to flow therepast, may be provided in the flow control component 404 or elsewhere in the system. A sensitive motion detector, such as a fetal heart monitor, may then be used to detect motion which results from flow, thus confirming that flow is occurring. Usually, it will be desirable to enhance the detectability of the flow responsive element. For example, the spring-loaded ball valve 440 may be formed from a magnetic material and/or impregnated with a ferromagnetic material to enhance detectability using a SQUID.

In other cases, flow may be detected by releasing a detectable substance, such as a non-toxic fluorescent or other dye marker, into the cerebrospinal fluid as it passes through the flow rate control component 404 or elsewhere in the catheter system. A reservoir of such detectable substance may be provided in the flow rate control module 404 and connected to a lumen or catheter which release small amounts of the detectable substance into the cerebrospinal fluid through the flow control module or associated catheter. The substance may then be detectable in a patient sample, such as blood, urine, saliva, or other easily accessible patient specimen which can then be assayed for presence of the substance. In any case, if it is determined that flow has ceased or become undetectable, it will be necessary to access the catheter system and correct the problem and/or replace components of the system.

The patient with Alzheimer's disease may be operated upon for implantation of the pressure driven pumps described above in the following manner: The patient will be completely anesthetized and intubated. The patient will be placed on the operating room table in the supine position. The scalp over the non-dominant parietal lobe will be shaved. An incision will be laid out over the parietal scalp, over the rib cage at about the mid-portion in the anterior axillary line, and in the abdomen. The three incision areas will be shaved, prepped, and draped in the usual fashion. The scalp incision will be open down to the bone and a burr hole placed. The area will be coagulated, and a conduit will be placed into the lateral ventricle on that side. Another incision will be made over the rib cage at roughly the T5 or T6 level. The incision will be made parallel to the rib at its upper portion. The rib will then be dissected free of the underlying pleura and the pump will be positioned against the internal side of the rib and held in place with sutures into the rib periosteum. Using a shunt-passing cannula, tubing will then be led from the conduit in the ventricle under the skin down to the pump and connected there. Again, an incision is made in the abdomen overlying the rectus muscle on the same side and the incision carried down to the peritoneum will then be opened and a conduit will be dropped into the peritoneum and also led subcutaneously up to the pump. After all the connections are made, all the skin incisions are closed in the usual fashion. The patient will be treated with preoperative antibiotics and then will probably spend a day or two in the hospital before going home. Implantation of the other embodiments will be apparent to those of ordinary skill in the art in view of the foregoing description.

It is also noted that an indicator may be coupled to any one of the pumps described 'above to provide an audible signal in response to detecting that the pump is pumping fluid. Alternatively, the ball valve pump configurations may comprise material to facilitate monitoring the pump with a stethoscope.

Claims

An apparatus for removing cerebrospinal fluid comprising:

a conduit comprising a first opening and a second opening, the first opening of the conduit being adapted to be disposed in fluid communication with a space within a patient's subarachnoid space, the second opening being adapted to be disposed in fluid communication with another portion of the patient's body; and

a flow rate control device attached to the conduit between the first and second openings, characterized in that the flow rate control device is a pump and an energy storage device and is adapted to permit flow of cerebrospinal fluid at a rate within the range of 0.5 ml/hr to 15 ml/hr based on the average removal rate over a 24 hour period, the apparatus being able to work under all physiologically expected cerebrospinal fluid volumes in a normal human subject in such period.
An apparatus of claim 1, further comprising a flow responsive element which provides a signal when flow passes through the flow rate control device.
An apparatus of claim 2, wherein the flow responsive element comprises a component which moves in response to flow, wherein said motion is detectable, e.g. magnetically detectable, or wherein the flow responsive element releases a detectable substance into fluid flowing through the flow rate control device.